Polyphase electric furnace.



.I. L. DIXON.

POLYPHASE ELECTRIC FURNACE.

ABPLICATION FILED JAN. 20. new.

Patented Dec. 4, 1917.

$51 atto'onu subject of the King of Great Britain, resid.

JOSEPH LAWTON DIXON, or DETROIT, MICHIGAN.

POLYPHASE ELECTRIC FURNACE.

Specification of Letters Patent.

Patented Dem 1,1917.

Application filed .Tanuary'20, 1917. Serial No. 143,467.

To all whom it may concern:

- Be it known that I, JOSEPH L. DIXON, a

ing at Detroit, county of Wayne, and State of Michigan, have invented certain new and useful Improvements in Polyphase Electric Furnaces, of which the following is a full, clear, and exact description.

The invention which forms the subject of my present application for Letters Patent is an improvement in means for the control of polyphase electric arc furnaces, and more particularly those which are, in the main,

characterized by the presence of three electrodes constituting the two outgoing and the common return terminals of a two phase three wire circuit, but its more general applicability to furnaces of a similar nature will beapparent from the tenor of the specification which follows. f

Furnaces of this general class have heretofbre been constructed with three electrodes placed above the bath or material to be treated, and connected up in a'three wire two phase system, in which event two electrodes are supplied with alternating currents differing in phase by 90 which are returned through the wire leading from the third elect-rode.

In such an arrangement it is necessary for the maintenance of the balance in the electrical system, that the common return electrode carry a current /2 times that in each of the other two electrodes, but this can occur only when there is no resistance between the bath of metal under treatment and the return electrode, or, in other words, when that electrode is in actual or direct contact with the material of the bath and not separated therefrom by an arc.

These conditions, incident to ordinary use, lead to dilliculties in the regulation of the electrodes, more especially so if such regulation is automatic and of the character which has heretofore been employed. Thus considering the case above discussed, 111 which there are three electrodes connected in a two phase three wire system, and assuming that automatic regulation is provided when the two main electrodes are each carrying a current of 5000 amperes, and the figures and the automatic controlling apparatus will cause all of the electrodes to approach nearer to the bath. The return electrode, however, is already touching the bath and anyforce tending to cause it to come into better contact with the same will result in either one or two things :should the metal beneath the said electrode be solid and therefore oppose any further downward movement of the electrode, a harmful strain will be thrown upon the gearing which tends to lower the electrode. On the other hand,

if the metal is liquid, the electrode will dip deeper into the bath and cause an undesired carburizing of the metal in the bath.

My present invention is designed to obviate such objections and to provide a means of automatic regulation not subject to the undesirable operations above described, and may be best described by reference to the diagramshown in the accompanying sheet of drawings. i

In this figure the furnace crucible or container is indicated by A, the meta-l bath by B, and the three electrodes by C, C and D. It may be assumed that E and Fare the coils of the generator or transformer which supplies two phase currents to the furnace, and from the connections shown it will be observed that they are those of the ordinary three Wire system in which the electrode D is connected to the common return or neutral I point G, the line conductors being designated H, K and L. Under .the conditions illustrated it is therefore the electrode D, which is that connected to the neutral point of the electrical system, that must be in direct electrical contact with the bath.

In carrying out my invention I place small transformers M, N and O in the lines or paths formed by the conductors H, K

and L, respectively, and provide that their secondary currents shall, in each case, be directly proportional to the currentln the primary conductors H, K and L with which they are connected. The transformers,

moreover, are so designed that all have the same ratio between their primary and secondary currents.

The secondary circuit of transformer N includes and energizes a solenoid P, and the secondary circuits of transformers M and 0 both include the coils of a solenoid R in a manner such. that the latter is energized by the vectorial sum of the currents/ supplied by the two transformers.

The magnetic effects of the two solenoids P and R are opposed to each other, the two having their armatures connected to a beam S pivoted at T and carrying atone end a contact between the two terminals of a circuit controller V. This device is, so arranged that when the two solenoids exert an equal pull neitherof the two contacts is closed, but either the upper or lower contact will be closed by the overbalancing magnetic effect of one of the solenoids.

Thus when the solenoid P exerts the stronger pull, the upper contact being closed, completes a circuit through any suitable device W in the nature of a controlling motor which in any proper and known way causes the electrode D to be raised. Similarly, when the solenoid R exerts the stronger pull, the lower contact is closed, causing the motor to operate in a manner to lower the electrode D.

l have not illustrated in any detail the special mechanism for accomplishing this object, beyond showing the motor, as there are many specific forms known and used for similar purposes and any suitable form may be adopted, nor have I deemed it necessary to illustrate the specific means for raising and lowering the electrode D, nor the elcc-' trodes C, C, as these are well known and commonly used, particularly those for the electrodes C which are or at least may be adjusted by hand.

The operation of the system, apparent from the above considerations, may be briefly described. Let it be assumed that the normal desired current in each of the electrodes C, C is '5000 amperes, and in D 45 times 5000, or approximately 7000 amperes. The current transformers M, N and 0 each have a ratio of 1000 to 1, so that when the electrodes are respectively carrying the above amounts of current, the solenoid P will be energized by a current of 7 amperes, and the vectorial sum or" the currents from the two transformers M and 0 will be 7 amperes which energizes the sole noid R, and therefore the pull of the two soleonids P and R will be balanced.

Now let it be assumed that the resistance of each of the arcs from electrodes C becomes increased so that the current in each falls to 2500 amperes, the electrode D remaining in contact with the liquid or solid bath and carrying its proper proportion of current, that is 3500 amperes. In sucl case the solenoids P and R are equally energized and therefore the electrode D is not lowered as it would be if automatically controlled by such apparatus as has heretofore, been employed.

A similar result will follow, that is the electrode D will not be lowered, whatever the actual amount-of current carried by that electrode, provided it is already in contact bath, then the solenoid R energized by the transformers M and 0 will overbalance the beam S, close the lower contact of the circuit controller and thus lower the electrode D.' A similar result will follow, that is the lowering of the electrode D, whatever the actual amount of'current it may be carry- .mg, provided it be out of actual contact with the bath and therefore carrying less than the correct relative amount.

In the above description of the invention it has been assumed that the object is to obtain a perfect balance ofthe electrical system by maintaining the electrode D in actual contact with the bath and at the same time to prevent any tendency for it to actually penetrate or dip into the bath. In some cases, however, such as the melting and refining of metals which have a strong ailinity for carbon, it may be desirable to prevent even the slightest contact of the electrode with the bath of metal, even though this would necessarily involvean unbalancing of the electrical system by causing the electrode D to carry a proportion of current less than 2 times the current in each of the other electrodes C.

This result may be attained by causing the solenoid P to exert a pull not equal to, but greater than solenoid B when the two are energized by equal currents. A similar re sult would be secured byconstrueting the transformers M, N and 0 so that they shall not have the same ratios, making M and O, for example, each of a ratio of 1000 to 1,

and the transformer N of some lesser ratio, as of 900 to 1. Furthermore, by means of well known devices such as ad ustab1e resistances in parallel with one or both of the solenoids P and R, the relative strengths of these solenoids may be adjustable at the will of the operator.

There are many modifications which may be made in the apparatus as I have some what specifically described it, without departure from the spirit of my invention, which, in essence, is the regulation of an electrode in a polyphase furnace, not in accordance with the actual amount of current carried by such an electrode, but in accord ance with the proportion of the current carried by it, relative to the total amount of current entering the furnace.

Furthermore, it is obvious that the apparatus I have described is applicable to polyphase furnaces of other types, for ex ample, three phase furnaces, but the application of my invention to such furnaces is .trodes connected to a polyphase system,

of the common return electrode or that which is permanently of the same potential v as the bath of metal in a polyphase electric furnace, which consists in adjusting such electrode in accordance .with the proportion of the current "which it carries, relative to the total amount of current entering the furnace. a

2. In a polyphase electric furnace, the combination with the crucible for containing a mass of material to be treated, of electhe different phases of and a common return electrode which is permanently'of the same potential as the bath and connected to the neutral 'point of the system, and means for adjusting the position ofthe return electrode dependent for operation on the-amount of current in said electrode relative to the total current supplied to the furnace.

3. In a polyphase electric furnace, the combination with a crucible for containing a mass of material to be treated, of three electrodes connected up in a two phase three wire system of current supply, means for adjusting the position of the common return electrode, and two opposing electro-magnets for controlling the operation of the same, energized normally and equally by current proportional to that through the return electrode and the vectorial sum of the currents proportional other electrodes.

4. In a polyphase electric furnace, the combination withthe crucible for containing a mass of material to be treated of upper electrodes, one for each phase and one connected with the neutral point of the system, of means for adjusting the position of the neutral electrode, and electromagnetic controlling means therefor, operated by the opposing energizing action of current proportional to that in the neutral electrode and by the vectorial sum of currents proportional to those in the other electrodes.

5. In a polyphase electric furnace, the combination with a crucible for containing the material to be treated of electrodes, one

for each phase of current and one connected to the neutral point of the system, of means for adjusting the position of the neutral electrode, and opposing solenoids for operating the same normally equally energized, respectively, by current induced by that in the neutral electrode and by the vectorial sum of currents induced by those in the other electrodes.

In testimony whereof I herewith afiix my signature.

- JOSEPH LAWTON DIXON.

Copies of this paten t may be obtained for five cents each, by addreulng the Gommluloner of ratentl Washington, D. 0.

to those through the 

